Re: [RFC PATCH v2 16/27] mm: Modify can_follow_write_pte/pmd for shadow stack

[Peter Zijlstra]

On Tue, Jul 10, 2018 at 03:26:28PM -0700, Yu-cheng Yu wrote:
> There are three possible shadow stack PTE settings:
> 
>   Normal SHSTK PTE: (R/O + DIRTY_HW)
>   SHSTK PTE COW'ed: (R/O + DIRTY_HW)
>   SHSTK PTE shared as R/O data: (R/O + DIRTY_SW)

I count _2_ distinct states there.

> Update can_follow_write_pte/pmd for the shadow stack.

So the below disallows can_follow_write when shstk && _PAGE_DIRTY_SW,
but this here Changelog doesn't explain why. Doesn't even get close.

Also, the code is a right mess :/ Can't we try harder to not let this
shadow stack stuff escape arch code.